This invention relates to a system for tracing a line or the edge of a line to activate an X-Y coordinate drive machine to follow a path described by the line. More particularly, the invention relates to a window generation circuit for use with an optical scanning head of such a system to inhibit the reception of incorrect image points.
Systems for tracing lines have been known for many years. However, such systems typically employ image sensing devices which require a mechanical rotation of a scanning head or the optics associated therewith to achieve satisfactory tracing. More recently, U.S. Pat. No. 4,049,962 which issued Sept. 20, 1977 in the name of the present inventor discloses a line edge follower wherein the image sensing head is operated electronically so as not to require mechanical rotation of the head or of optical elements therein. Electronic scanning of a circular array of photodiodes extracts the requisite points of an image of the line being traced for producing the necessary drive signals which activate the motors of the coordinate drive.
The description of the line edge follower disclosed in the foregoing U.S. Pat. No. 4,049,962 is hereby incorporated by reference.
In use, such a tracing machine may be employed to position a cutting tool on a workpiece in the metallurgical arts by following along a line on a template. The cutting machine may also be used in cutting other materials as well as in scribing markings on various materials.
While the tracing machine disclosed in the foregoing patent operates satisfactorily, a problem has been noticed in the case of a defective template wherein a break is found in the line being traced. Due to the circular scanning of the photodiodes about the circular array, as the machine advances along the template line, image points of the broken portion of the line are detected by the scanned array. The absence of an image point designating the presence of the line, at the location of the break, sensitizes the system to an image point of the line at another location within the scan. Resulting motor drive signals have directed the motors to rotate in the reverse direction with a consequent damaging of the workpiece.